1. Field of the Invention
This invention relates to medical diagnostic devices and procedures which monitor or evaluate conditions within a body by means of externally positioned apparatus. Specifically, this invention relates to devices which are structured to provide self-adherence of a diagnostic device to a patient's skin through employment of a coupling medium having adherent properties in relation to the skin of the patient.
2. Statement of the Art
Many medical diagnostic devices are used externally to a patient's body to evaluate or monitor conditions which exist within the patient's body. A common example of such devices are ultrasound apparatus. Ultrasound refers to sound waves the frequencies of which are above those perceptible by the human ear. Because body tissues are generally good conductors of ultrasound, diagnostic methods using ultrasound are often used in medicine. In particular, sound waves with frequencies above one Megahertz (1 Mhz.) can be used to probe internal structures in the human body. During ultrasonic monitoring, high frequency sound waves are transmitted through the body from a source external to the body. By measuring the time and amplitude of sound waves reflected back to an ultrasonic sensor, one can measure tissue density and tissue movement. In most monitors, the ultrasonic transmitter and receiver are combined into a single transducer.
Ultrasound is used medically for imaging, fetal heart rate monitoring, air embolism detection and arterial mapping, and other applications. Of these applications, all but imaging are based on the Doppler effect. The Doppler effect is a detectable shift in frequency of the waves emanating from a moving object and can be used to determine the relative movement of that object. In fetal heart rate monitoring, for example, the Doppler shift principle is applied to detect shifts in frequency of ultrasound waves reflected from the moving valves of the fetal heart to determine fetal heart rate (FHR). In other medical monitoring applications, the Doppler shift occurs when ultrasound waves are reflected from moving blood cells in an artery or in the heart.
Specifically with respect to non-invasive FHR monitoring, an ultrasound device, including a transmitter and receiver, is positioned against the mother's abdomen and ultrasound waves are emitted into the body in the area of the fetus. The signal is continuously transmitted and reflected signals are continuously received. If the reflecting surface is not in motion, the frequency of the two signals remains the same. However, when the transmitted signal is reflected off a moving surface, such as the fetal heart, a frequency shift occurs. The detected frequency shift is converted to an electronic signal and is amplified so that the shift may be heard or visualized, or both.
Certain problems are encountered in ultrasound FHR monitoring one of the most significant being that the ultrasound often detects movement of maternal blood vessels in the area of the uterus and the signals can be confusing. It is necessary therefore, to move the ultrasound device around the area of the patient's abdomen until a strong signal is detected from the fetal heart. If the mother or fetus moves, the signal may be lost and the ultrasound device may have to be shifted again to obtain the best signal.
Once a strong signal is detected, the ultrasound device must be held in place during the monitoring session. That is accomplished either by holding the device in place by hand or by strapping the device to the patient by means of a belt encircling the body of the patient. Since monitoring sessions can last an hour or longer, holding the ultrasound device by hand can be uncomfortable and inconvenient. However, strapping the device to the patient may be uncomfortable for the patient and requires occasional adjustment.
The problems of strapping external medical devices to a patient's abdomen has been addressed in U.S. Pat. No. 5,070,888 to Hon, et al., issued Dec. 10, 1991 in which is disclosed a tocodynamometer having a concave support base for application to the patient's abdomen. The Hon device employs a sheet of adhesive material covering the support base and requires the application of an adhesive binder solution to the abdomen of the patient to effect bonding. The Hon device does not accommodate the continuous movement of the device about the patient's abdomen.
A second concern in conducting ultrasound diagnosis is the problem associated with the coupling medium used to contact the ultrasound device with the patient's skin. That is, it is necessary in performing an ultrasound procedure to have proper acoustical coupling between the ultrasound transducer and the patient's skin to facilitate transmission of the sound wave through the skin and other body tissues. If, for example, air pockets form between the ultrasound transducer and the patient's skin, the sound wave is merely deflected back to the transducer without passing into the body because air is less dense than tissue. Therefore, it is important to provide a coupling medium between the transducer and the patient's skin which is acoustically compatible, or which has a density similar to body tissue, in order to optimize transmission of the sound waves.
In prior art devices and procedures, a fluid-like transmission gel is applied to the patient's skin in the area of treatment, and the ultrasound transducer is moved over the gel and over the patient's skin until a desired signal is obtained. Such gels are messy and preclude adhesion to the skin using conventional adhesives.
In view of the foregoing problems associated with ultrasound diagnosis, it would be advantageous to provide an ultrasound device which is structured to provide self-adherence of the device to the patient's skin thereby freeing the user's hands after positioning. It would further be advantageous to provide an ultrasound device which employs a coupling medium having inherent self-adherent properties and which provides consistent contact with the patient's skin to ensure proper transmission of the wave signal, and which reduces or eliminates the need for messy fluid-type gels.